OSLO, Nov 29 (Reuters) - Hexagon Chief Executive Ola Rollen, on trial in Norway for suspected insider share trading, should be sentenced to 18 months in prison if found guilty, the prosecutor in the case told the court on Wednesday.

One of Sweden's best known business leaders, Rollen has pleaded not guilty to charges stemming from the purchase of shares in Norway's Next Biometrics in 2015, a transaction which did not involve Hexagon.

"Rollen has described himself as a professional investor, he has been the CEO of Hexagon for many years and in this regard he has bought many companies," prosecutor Marianne Bender told the court.

"More than most, he is well aware of what affects share prices," she said. "This must be a significantly aggravating factor in the sentencing."

The maximum sentence the prosecution could have asked for was six years in prison.

The prosecution also requested the confiscation of 25 million Norwegian crowns ($3 million) in gains from the shares.

Hexagon's shares fell on the news, trading 1.4 percent lower for the day at 1415 GMT, while shares of Next Biometrics fell by 2.4 percent.

Bender said Rollen's purchase of Next shares on Oct. 6 and 7, 2015 on behalf of Greenbridge, an investment firm he co-founded, was illegal as Greenbridge was also involved in talks to take a larger stake in Next at a higher price.

Rollen's lawyer argued, however, that his client did not possess privileged information at the time of the share purchase and that the transactions were motivated by his own independent analysis of Next Biometrics.

Rollen's lawyer will deliver his closing arguments on Thursday. A verdict is expected in early 2018.